In a so-called indirect-type AC power converting apparatus, a large-size capacitor is provided at a so-called DC link between a converter and an inverter. This capacitor has a function to smooth a voltage ripple caused by the commercial frequency. This technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-224393 (1997). According to this document, an inverter section for a compressor and an inverter section for a fan are connected in parallel with respect to a smoothing capacitor, to thereby share a power source between both of the inverter sections. In this technique, a DC voltage is shared between both of the inverters, and therefore a control of the fan is corrected in accordance with the DC voltage which varies in accordance with a load of the compressor.
On the other hand, in a direct-type AC power converting apparatus, a large-size capacitor or reactor is not required. Therefore, in this converting apparatus, downsizing can be expected, and in recent years, there has been an increasing interest in it as a next-generation power converting apparatus. For example, in Japanese Patent Application Laid-Open No. 2007-312589, one inverter is connected to one converter. There is introduced a technique (hereinafter, sometimes represented simply as “a commutation in a converter at a zero current”) of causing a commutation in the converter when the inverter is operated based on a zero vector and a so-called zero-current state is established. There is also introduced a technique by which a carrier can be shared between the converter and the inverter.
As for the direct-type AC power converting apparatus, a technique has also been proposed in which an operation is performed with a plurality of inverters being connected with respect to one converter for the purpose of increasing an output power capacity. This technique is disclosed in, for example, Kato and Ito, “Improvement of Waveform for a Boost type AC/DC/AC Direct Converter”, Institute of Electrical Engineers of Japan, national convention 2007/3/15-17, Part 4, 4-098. In this document, a current-source rectifier can be recognized as a converter, and a DC/DC converter can be recognized as an inverter. The DC/DC converter and a voltage-source inverter are connected in parallel. According to the technique shown in this document, a commutation is caused in the current-source rectifier at a so-called zero current, and thus a plurality of inverters are controlled by a pulse-width modulation by a single carrier synchronized with a carrier based on which the current-source rectifier is operated.
From the viewpoint of increasing an output power capacity, a technique has been proposed in which a plurality of matrix converters are connected in parallel with respect to one LC filter and furthermore are connected in parallel with respect to one load (see Japanese Patent Application Laid-Open No. 2005-65356 and Ayano, Inaba, and Ogasawara, “Reduction Effect of EMI in Parallel Matrix Converter Systems”, Journal of IEEJ, D, Vol. 128, No. 3, pp. 184 to 192 (2008)).
Ogasawara, Fujita, and Akagi, “Modeling and Analysis of High-Frequency Leakage Currents Caused by Voltage-Source PWM Inverters”, Journal of IEEJ, D, Vol. 115, No. 1, pp. 77 to 83 (1995) mentions a common-mode voltage of an inverter which is controlled by a pulse-width modulation.
Japanese Patent Publication No. 6-81514 (1994) discloses a waveform subjected to a three-phase modulation which will be described later.